Mask blank, transfer mask, method of manufacturing a transfer mask, and method of manufacturing a semiconductor device

ABSTRACT

A mask blank for use in the manufacture of a binary mask adapted to be applied with ArF excimer laser exposure light has, on a transparent substrate, a light-shielding film for forming a transfer pattern. The light-shielding film has a laminated structure of a lower layer and an upper layer and has an optical density of 2.8 or more for exposure light and a thickness of 45 nm or less. The lower layer is made of a material in which the total content of a transition metal and silicon is 90 at % or more, and has a thickness of 30 nm or more. The upper layer has a thickness of 3 nm or more and 6 nm or less. The phase difference between exposure light transmitted through the light-shielding film and exposure light transmitted in air for a distance equal to the thickness of the light-shielding film is 30 degrees or less.

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2010-221661, filed on Sep. 30, 2010, thedisclosure of which is incorporated herein in its entirety by reference.

TECHNICAL FIELD

This invention relates to a mask blank and a transfer mask for use inthe manufacture of semiconductor devices or the like and further relatesto a method of manufacturing a transfer mask and a method ofmanufacturing a semiconductor device.

BACKGROUND ART

The miniaturization of semiconductor devices and the like isadvantageous in bringing about an improvement in performance andfunction (higher-speed operation, lower power consumption, etc.) and areduction in cost and thus has been accelerated more and more. Thelithography technique has been supporting this miniaturization andtransfer masks are a key technique along with exposure apparatuses andresist materials.

In recent years, the development of the DRAM half-pitch (hp) 45 nm to 32nm generations according to the semiconductor device design rule hasbeen progressing. This corresponds to about ¼ to ⅙ of a wavelength 193nm of ArF excimer laser exposure light (hereinafter referred to as “ArFexposure light”). Particularly, in the DRAM hp45 nm and subsequentgenerations, only the application of the resolution enhancementtechnology (RET) such as the conventional phase shift method, obliqueincidence illumination method, and pupil filter method and the opticalproximity correction (OPC) technique has been becoming insufficient andthe hyper-NA (numerical aperture) technique (immersion lithography) hasbeen becoming necessary.

In the meantime, circuit patterns necessary in the manufacture ofsemiconductor devices are formed in sequence by exposing a photomask(reticle) pattern a plurality of times onto a semiconductor wafer. Forexample, a reduced projection exposure apparatus (exposure apparatus)with a predetermined reticle set therein repeatedly projects and exposesa pattern of the reticle while sequentially shifting a projection areaon a semiconductor wafer (step-and-repeat system), or repeatedlyprojects and exposes a pattern of the reticle while synchronouslyscanning the reticle and a semiconductor wafer with respect to aprojection optical system (step-and-scan system). These systems havebeen predominant. As a consequence, a predetermined number of integratedcircuit chip areas are formed in the wafer.

A photomask (reticle) has an area formed with a transfer pattern and aperipheral area around the transfer pattern area, i.e. an edge areaalong four sides in the photomask (reticle). When exposing the transferpattern of the photomask (reticle) while sequentially shifting aprojection area on a semiconductor wafer, the transfer pattern isexposed and transferred to the projection areas so that the photomaskperipheral areas overlap each other for the purpose of increasing thenumber of integrated circuit chips to be formed. Normally, a mask stageof an exposure apparatus is provided with a shielding plate for blockingirradiation of exposure light onto the photomask peripheral area.However, in the case of blocking the irradiation of the exposure lightby the shielding plate, there are problems of positional accuracylimitation and of light diffraction phenomenon so that it is notpossible to avoid leakage of the exposure light to the photomaskperipheral area (hereinafter, this exposure light will be referred to as“leakage light”). If this leakage light to the photomask peripheral areais transmitted through the photomask, there is a possibility ofsensitizing a resist on the wafer.

In order to prevent the sensitization of the resist on the wafer due tosuch overlapping exposure, a light-shielding band (a band of shieldingmaterial or light-shielder ring) is formed in the photomask peripheralarea by mask processing. Normally, it is reported that, in an area,where the light-shielding band is formed, of the photomask peripheralarea, an OD value (optical density) of 3 or more is desirable and thatof at least about 2.8 is necessary for preventing the sensitization ofthe resist on the wafer due to the overlapping exposure.

In the case of a binary mask, since the light-shielding performance of alight-shielding film is high, the light-shielding film serves to form alight-shielding film pattern in a transfer pattern area and further toform a light-shielding band in a peripheral area around the transferpattern area.

The light-shielding film is also required to have a certain lowfront-surface reflectance for exposure light. In view of this, thelight-shielding film generally has a laminated structure of at least twolayers, i.e. a layer for ensuring the light-shielding performance and alayer (front-surface antireflection layer) for reducing thefront-surface reflectance. The front-surface antireflection layer has adifficulty in enhancing the light-shielding performance in terms of itsproperties and thus cannot contribute to a reduction in the thickness ofthe light-shielding film. The reduction in the thickness of thelight-shielding film has these restrictions.

When the thickness of the light-shielding film is reduced, the OD(optical density) value is also reduced. In the case of a chromium-basedlight-shielding film, the total thickness of about 60 nm is minimallyrequired for achieving OD=3 which is generally required, and therefore,a large reduction in the thickness of the film is difficult to achieve(see, e.g. Patent Document 1: JP-A-2007-241136, paragraph [0005]).

Further, also in the case of, for example, a so-called binary photomaskcomprising a light-shielding film having a laminated structure ofMoSi-based materials, such as a light-shielding film having a laminatedstructure of a MoSiN light-shielding layer and a MoSiON antireflectionlayer from the substrate side, the total thickness of normally about 60nm is minimally required for achieving OD=2.8 which is required, andtherefore, a large reduction in the thickness of the film is difficultto achieve (Patent Document 2: JP-A-2006-78825).

On the other hand, Patent Document 3 (WO2005/124464) discloses a maskblank comprising a light-semitransmissive film. Thislight-semitransmissive film has a property of transmitting exposurelight at a predetermined transmittance and this property issubstantially the same as that of a conventional halftone phase shiftfilm. However, this light-semitransmissive film also has a property suchthat the phase difference between exposure light transmitted through alight-semitransmissive portion formed with the light-semitransmissivefilm and exposure light transmitted through a light-transmissive portionformed with no light-semitransmissive film is small. This property istotally different from that of the conventional halftone phase shiftfilm. The mask blank comprising this light-semitransmissive film is usedfor manufacturing an enhancer mask.

SUMMARY OF THE INVENTION

In the meantime, in binary masks in the DRAM half-pitch (hp) 40 nm andsubsequent generations according to the semiconductor device designrule, the line width of a transfer pattern of a transfer mask is smallerthan the wavelength 193 nm of ArF exposure light and, as a result ofadopting the resolution enhancement technology for coping with it, therehas arisen a problem that if the thickness of a light-shielding filmpattern in a transfer pattern area (main pattern area) is large, a bias(correction amount of pattern line width or the like) due to theelectromagnetic field (EMF) effect becomes large. A bias due to the EMFeffect largely affects the CD accuracy of the line width of a transferpattern onto a resist on a semiconductor wafer. Therefore, in order tosuppress the influence due to the EMF bias, it is necessary to carry outsimulation of the EMF effect, thereby performing correction of atransfer pattern to be formed in a transfer mask when manufacturing thetransfer mask. Calculation of this transfer pattern correction becomesmore complicated as the EMF bias increases. Further, a transfer patternafter the correction also becomes more complicated as the EMF biasincreases. As a consequence, a large load is applied to the manufactureof the transfer mask. These new problems have arisen due to the increasein EMF bias.

Optical simulation in mask design of a binary mask is largely aimed atcalculating a shape of a correction pattern such as OPC (opticalproximity correction) or SRAF (sub-resolution assist features) to beadditionally disposed, a correction amount (bias amount) of pattern linewidth, and so on so that a designed transfer pattern is exposed andtransferred to a transfer object (resist on a wafer, or the like) asdesigned. As this mask-design optical simulation, there is TMA (thinmask analysis). TMA calculates a shape of a correction pattern and acorrection amount of pattern line width assuming that a light-shieldingfilm of a transfer mask is an ideal film that has a predeterminedoptical density with its thickness being zero. Because of the simplesimulation being carried out with the ideal film, there is a large meritthat the calculation load of the simulation is small. However, sincethis is the simulation that does not take into account the EMF effect,the TMA simulation results alone are insufficient for a recent finepattern which is largely affected by the EMF effect.

The present inventors have intensively studied the subject of theabove-mentioned EMF effect.

First, the present inventors have paid attention to the fact that, inthe case of a light-shielding film with a small influence of the EMFeffect, it is easy to take advantage of the TMA simulation and thus toreduce the load of EMF bias correction calculation.

As a result of further studying a light-shielding film with a smallinfluence of the EMF effect, it has been found that, even in the case ofa binary transfer mask, the phase difference between exposure lighttransmitted through a light-shielding portion formed with alight-shielding film and exposure light transmitted through alight-transmissive portion formed with no light-shielding film(hereinafter, this phase difference will be referred to simply as a“phase difference”) is related to the influence of the EMF effect.Specifically, it has been found by simulation that as the phasedifference of the light-shielding film decreases, the EMF bias alsodecreases.

Further, it has been found that the thickness of the light-shieldingfilm is also related to the EMF bias. Specifically, if the thickness ofthe light-shielding film is less than 50 nm, the load of transferpattern correction calculation for correcting the influence of the EMFbias becomes small and thus the transfer mask manufacturing load alsobecomes small. Further, if the thickness of the light-shielding film is47 nm or less, the EMF bias can be considerably reduced. Further, if thethickness of the light-shielding film is 40 nm or less, a moresignificant EMF bias reducing effect can be obtained. These results havebeen made clear by simulation.

In layers forming the light-shielding film, a front-surfaceantireflection layer as an upper layer is required to have anantireflection function and thus is required to contain a certain ormore amount of oxygen and/or nitrogen so that the refractive indexthereof inevitably becomes high. Therefore, the front-surfaceantireflection layer serves to produce a large plus-direction phasedifference. In order to provide the front-surface antireflection layerwith the antireflection function, the front-surface antireflection layershould be formed of a material with a small extinction coefficient k.Since most of the light-shielding performance of the entirelight-shielding film should be achieved by a light-shielding layer as alower layer, the light-shielding layer should be formed of a materialwith a large extinction coefficient k.

Taking these into account, first, a material with a small refractiveindex n and with a large extinction coefficient k has been selected asthe light-shielding layer (lower layer). It has been found that thematerial having such properties is a transition metal silicide-basedmaterial in which the content of other components (particularly oxygenand/or nitrogen) adapted to increase the refractive index n of thematerial or to reduce the extinction coefficient k of the material islimited to less than 10 at %. That is, as the material forming thelight-shielding layer, a selection has been made of a material in whichthe total content of a transition metal and silicon is 90 at % or more.

Next, a study has been made of a film structure that simultaneouslysatisfies three conditions that the total thickness of thelight-shielding film is 45 nm or less, that the optical density thereoffor exposure light is 2.8 or more, and that the phase difference thereofis 30 degrees or less. It has been found that, in order to achieve theoptical density of 2.8 or more in the laminated structure with thefront-surface antireflection layer having a low optical density whilethe thickness of the entire light-shielding film is 45 nm or less, thelight-shielding layer (lower layer) formed of the above-mentionedmaterial should have a thickness of at least 30 nm. The light-shieldinglayer of this thickness serves to produce only a small minus-directionphase difference. As a consequence, if the thickness of thefront-surface antireflection layer is set to a conventional thickness,the phase difference over the entire light-shielding film largelyexceeds plus 30 degrees. On the other hand, owing to the development ofexposure apparatuses in recent years, the influence of front-surfacereflection from a light-shielding film upon exposure and transfer hasbeen decreasing so that even if the front-surface reflectance is more orless greater than conventional, it tends to be allowed. Taking theseinto account, as a result of loosely setting the front-surfacereflectance of the light-shielding film to less than 50% and making astudy, it has been found that, using the selected material of thelight-shielding layer, if the thickness of the front-surfaceantireflection layer is 3 nm or more, the front-surface reflectance canbe set to less than 50%. It has also been found that if the thickness ofthe front-surface antireflection layer is 6 nm or less, the phasedifference over the entire light-shielding film can be suppressed towithin 30 degrees.

Synthetically taking into account the results of various studiesdescribed above, this invention has been completed.

It is an object of this invention to provide a mask blank whichcomprises a light-shielding film with a reduced EMF bias so that variousloads applied to the manufacture of a transfer mask are largely reduced,and which can simultaneously satisfy a condition that when the maskblank is formed into the transfer mask, the light-shielding film ensuresan optical density that can prevent sensitization of a resist film on asemiconductor wafer due to leakage light caused by overlapping exposure,and further to provide such a transfer mask, a method of manufacturingsuch a transfer mask, and a method of manufacturing a semiconductordevice using such a transfer mask.

This invention has the following structures.

(Structure 1)

A mask blank for use in the manufacture of a binary mask adapted to beapplied with ArF excimer laser exposure light, the mask blankcomprising, on a transparent substrate, a light-shielding film forforming a transfer pattern,

wherein the light-shielding film has a laminated structure of alight-shielding layer (lower layer) and a front-surface antireflectionlayer (upper layer) and has an optical density of 2.8 or more for theexposure light and a thickness of 45 nm or less,

the light-shielding layer (lower layer) is made of a material in whichthe total content of a transition metal and silicon is 90 at % or more,and has a thickness of 30 nm or more,

the front-surface antireflection layer (upper layer) has a thickness of3 nm or more and 6 nm or less, and

a phase difference between the exposure light transmitted through thelight-shielding film and the exposure light transmitted in air for adistance equal to the thickness of the light-shielding film is 30degrees or less.

(Structure 2)

The mask blank according to Structure 1, wherein a ratio obtained bydividing a content of the transition metal in the light-shielding layer(lower layer) by the total content of the transition metal and siliconin the lower layer is 42% or less.

(Structure 3)

The mask blank according to Structure 1 or 2, wherein the transitionmetal in the light-shielding layer (lower layer) is molybdenum (Mo).

(Structure 4)

A mask blank for use in the manufacture of a binary mask adapted to beapplied with ArF excimer laser exposure light, the mask blankcomprising, on a transparent substrate, a light-shielding film forforming a transfer pattern,

wherein the light-shielding film has a laminated structure of alight-shielding layer (lower layer) and a front-surface antireflectionlayer (upper layer) and has an optical density of 2.8 or more for theexposure light and a thickness of 45 nm or less,

the light-shielding layer (lower layer) is made of a material having arefractive index n of less than 2.00 and an extinction coefficient k of2.37 or more and has a thickness of 30 nm or more,

the front-surface antireflection layer (upper layer) has a thickness of3 nm or more and 6 nm or less, and

a phase difference between the exposure light transmitted through thelight-shielding film and the exposure light transmitted in air for adistance equal to the thickness of the light-shielding film is 30degrees or less.

(Structure 5)

The mask blank according to any of Structures 1 to 4, wherein thefront-surface antireflection layer (upper layer) is made of a materialhaving a refractive index n of 2.00 or more and an extinctioncoefficient k of 1.00 or less.

(Structure 6)

The mask blank according to any of Structures 1 to 5, wherein thelight-shielding layer (lower layer) has a thickness of 42 nm or less.

(Structure 7)

The mask blank according to any of Structures 1 to 6, wherein thefront-surface antireflection layer (upper layer) is composed mainly of

a material containing a transition metal, silicon, and at least oneelement from oxygen and nitrogen,

a material containing silicon and at least one element from oxygen andnitrogen, or

a material containing a transition metal and at least one element fromoxygen and nitrogen.

(Structure 8)

The mask blank according to Structure 7, wherein the transition metal inthe front-surface antireflection layer (upper layer) is molybdenum (Mo).

(Structure 9)

A method of manufacturing a transfer mask, comprising an etching step ofpatterning, by etching, the light-shielding film in the mask blankaccording to any of Structures 1 to 8.

(Structure 10)

A binary transfer mask adapted to be applied with ArF excimer laserexposure light, the transfer mask comprising, on a transparentsubstrate, a light-shielding film having a transfer pattern,

wherein the light-shielding film has a laminated structure of alight-shielding layer (lower layer) and a front-surface antireflectionlayer (upper layer) and has an optical density of 2.8 or more for theexposure light and a thickness of 45 nm or less,

the light-shielding layer (lower layer) is made of a material in whichthe total content of a transition metal and silicon is 90 at % or more,and has a thickness of 30 nm or more,

the front-surface antireflection layer (upper layer) has a thickness of3 nm or more and 6 nm or less, and

a phase difference between the exposure light transmitted through thelight-shielding film and the exposure light transmitted in air for adistance equal to the thickness of the light-shielding film is 30degrees or less.

(Structure 11)

A binary transfer mask adapted to be applied with ArF excimer laserexposure light, the transfer mask comprising, on a transparentsubstrate, a light-shielding film having a transfer pattern,

wherein the light-shielding film has a laminated structure of alight-shielding layer (lower layer) and a front-surface antireflectionlayer (upper layer) and has an optical density of 2.8 or more for theexposure light and a thickness of 45 nm or less,

the light-shielding layer (lower layer) is made of a material having arefractive index n of less than 2.00 and an extinction coefficient k of2.37 or more and has a thickness of 30 nm or more,

the front-surface antireflection layer (upper layer) has a thickness of3 nm or more and 6 nm or less, and

a phase difference between the exposure light transmitted through thelight-shielding film and the exposure light transmitted in air for adistance equal to the thickness of the light-shielding film is 30degrees or less.

(Structure 12)

The binary transfer mask according to Structure 10 or 11, wherein thetransfer pattern of the light-shielding film includes a line & spacepattern of half-pitch 40 nm or less.

(Structure 13)

A method of manufacturing a semiconductor device, comprising forming acircuit pattern on a semiconductor wafer using the binary transfer maskaccording to any of Structures 10 to 12,

(Structure 14)

The method according to Structure 13, wherein the circuit pattern formedon the semiconductor wafer includes a line & space pattern of half-pitch40 nm or less.

According to this invention, it is possible to realize and provide alight-shielding film with a reduced EMF bias so that various loadsapplied to the manufacture of a transfer mask are largely reduced.Further, this light-shielding film with the reduced EMF bias cansimultaneously satisfy a condition that the light-shielding film ensuresan optical density that can prevent sensitization of a resist film on asemiconductor wafer due to leakage light caused by overlapping exposure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the relationships between the full pitch oftransfer patterns in a plurality of kinds of light-shielding filmsadapted to produce different phase differences and the EMF bias;

FIG. 2 is a graph showing the relationships between the phase differenceof light-shielding films and the EMF bias;

FIG. 3 is a graph showing the relationships between the thickness offront-surface antireflection layers and the phase difference oflight-shielding films and the relationships between the thickness offront-surface antireflection layers and the front-surface reflectancefor exposure light;

FIG. 4 is a graph showing the relationships between the thickness offront-surface antireflection layers and the EMF bias;

FIG. 5 is a graph showing EMF biases due to refractive indices n andextinction coefficients k of light-shielding layers by sizes of bubblesin the case where the full pitch of a transfer pattern is 80 nm;

FIG. 6 is a graph showing EMF biases due to refractive indices n andextinction coefficients k of light-shielding layers by sizes of bubblesin the case where the full pitch of a transfer pattern is 100 nm;

FIG. 7 is a graph showing EMF biases due to refractive indices n andextinction coefficients k of light-shielding layers by sizes of bubblesin the case where the full pitch of a transfer pattern is 120 nm;

FIG. 8 is a graph showing the relationship between the thickness oflight-shielding films and the EMF bias in the case where light-shieldinglayers have the same refractive index n;

FIG. 9 is a graph showing the relationships between the extinctioncoefficient k and thickness of light-shielding layers and the opticaldensity thereof;

FIG. 10 is a graph showing the relationships between the Mo/(Mo+Si)ratio in molybdenum silicide films and the refractive index n andextinction coefficient k of the films;

FIG. 11 is a graph showing the results of examining how the totalthickness, the total phase shift amount, the total OD, and thefront-surface reflectance respectively change when the upper layerthickness and the lower layer thickness of a light-shielding film arerespectively changed in Example 1 of this invention;

FIG. 12 is a graph showing the results of examining how the totalthickness, the total phase shift amount, the total OD, and thefront-surface reflectance respectively change when the upper layerthickness and the lower layer thickness of a light-shielding film arerespectively changed in Example 2 of this invention;

FIG. 13 is an exemplary cross-sectional view showing a mask blankaccording to an embodiment of this invention; and

FIG. 14 shows exemplary cross-sectional views for explainingmanufacturing processes of a transfer mask according to an Example ofthis invention.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

Hereinbelow, this invention will be described in detail.

A mask blank according to this invention is for use in the manufactureof a binary mask adapted to be applied with ArF excimer laser exposurelight, the mask blank comprising, on a transparent substrate, alight-shielding film for forming a transfer pattern,

wherein the light-shielding film has a laminated structure of alight-shielding layer (lower layer) and a front-surface antireflectionlayer (upper layer) and has an optical density of 2.8 or more for theexposure light and a thickness of 45 nm or less,

the light-shielding layer (lower layer) is made of a material in whichthe total content of a transition metal and silicon is 90 at % or more,and has a thickness of 30 nm or more,

the front-surface antireflection layer (upper layer) has a thickness of3 nm or more and 6 nm or less, and

a phase difference between the exposure light transmitted through thelight-shielding film and the exposure light transmitted in air for adistance equal to the thickness of the light-shielding film is 30degrees or less.

Further, a mask blank according to this invention is also for use in themanufacture of a binary mask adapted to be applied with ArF excimerlaser exposure light, the mask blank comprising, on a transparentsubstrate, a light-shielding film for forming a transfer pattern,

wherein the light-shielding film has a laminated structure of alight-shielding layer (lower layer) and a front-surface antireflectionlayer (upper layer) and has an optical density of 2.8 or more for theexposure light and a thickness of 45 nm or less,

the light-shielding layer (lower layer) is made of a material having arefractive index n of less than 2.00 and an extinction coefficient k of2.37 or more and has a thickness of 30 nm or more,

the front-surface antireflection layer (upper layer) has a thickness of3 nm or more and 6 nm or less, and

a phase difference between the exposure light transmitted through thelight-shielding film and the exposure light transmitted in air for adistance equal to the thickness of the light-shielding film is 30degrees or less.

According to each structure mentioned above, it is possible to realizeand provide a light-shielding film with a reduced EMF bias so thatvarious loads applied to the manufacture of a transfer mask are largelyreduced. Further, this light-shielding film with the reduced EMF biascan simultaneously satisfy a condition that the light-shielding filmensures an optical density (2.8 or more) that can prevent sensitizationof a resist film on a semiconductor wafer due to leakage light caused byoverlapping exposure.

FIG. 1 shows the results of calculating, by simulation, EMF biases thatare generated when transfer masks respectively having line & spacepatterns (transfer patterns) of various pattern pitches inlight-shielding films (OD is 2.8 or more) adapted to produce variousphase differences were manufactured and the line & space patterns wereeach exposed and transferred to an object (resist film on asemiconductor wafer, or the like). In this simulation, the calculationwas carried out by setting the illumination condition of ArF exposurelight to annular illumination. In the graph, the pitch on the abscissaaxis represents the full pitch of a line & space pattern to be exposedand transferred to the object.

From FIG. 1, it can be first said that, in the case of anylight-shielding film adapted to produce any phase difference, the EMFbias increases as the full pitch of the line & space pattern decreases.In particular, the EMF bias rapidly increases between the full pitchesof 90 nm and 80 nm. On the other hand, as the phase difference of thelight-shielding film decreases, the EMF bias decreases. In this case, asthe pattern pitch width decreases, the reduction degree of the EMF biasis more significant. In particular, in the case of the light-shieldingfilm adapted to produce a small phase difference, the increase degree ofthe EMF bias is largely improved between the full pitches of 90 nm and80 nm. From these results, it is clear that the reduction in the phasedifference of the light-shielding film largely contributes to thereduction in EMF bias.

In order to form a light-shielding film adapted to produce a small phasedifference, it is necessary to use a material with a small refractiveindex. However, in general, the light-shielding film is provided with afront-surface antireflection layer for suppressing the front-surfacereflection for exposure light. As a material of the front-surfaceantireflection layer, use is made of a material containing a relativelylarge amount of oxygen and/or nitrogen and thus having a largerefractive index. Therefore, under the following conditions, simulationwas carried out for EMF biases which are generated when transfer maskseach having a transfer pattern in a light-shielding film with alaminated structure of a light-shielding layer and a front-surfaceantireflection layer were manufactured and the transfer patterns wereeach exposed and transferred to an object. Simulation of thefront-surface reflectance for exposure light was also carried out inparallel. In these simulations, the properties of a material of thefront-surface antireflection layers were fixed to a refractive index nof 2.35 and an extinction coefficient k of 0.99, while the thicknessesof the front-surface antireflection layers were set to be different fromeach other by 2 nm in the range of 0 to 20 nm. As materials of thelight-shielding layers, a selection was made of three material/thicknessconditions, i.e. Condition 1 (n=1.50, k=2.66, thickness=40 nm),Condition 2 (n=1.50, k=2.14, thickness=50 nm), and Condition 3 (n=2.00,k=2.58, thickness=40 nm), which were respectively simulated. Thematerial and thickness of the light-shielding layer were selected suchthat a predetermined optical density (OD: 2.8 or more) could be ensuredonly by the light-shielding layer. A transfer pattern to be exposed andtransferred to an object using the transfer mask was a line & spacepattern with a full pitch of 80 nm. Accordingly, the space width of thetransfer pattern formed in the light-shielding film of the transfer maskis 160 nm as a design value before correction. The illuminationcondition of ArF exposure light was set to annular illumination.

FIG. 2 shows the relationships between the phase difference of theentire light-shielding films and the EMF bias, using the simulationresults. From FIG. 2, it is seen that, in the case of using any ofConditions 1 to 3 of the light-shielding layers, the EMF bias decreasesas the phase difference over the entire light-shielding film decreases.

FIG. 3 shows, in one graph, the relationships between the thickness ofthe front-surface antireflection layers (AR layers) and the phasedifference of the entire light-shielding films and the relationshipsbetween the thickness of the front-surface antireflection layers and thefront-surface reflectance for the exposure light, using the samesimulation results. From FIG. 3, it is seen that, in the case of usingany of Conditions 1 to 3 of the light-shielding layers, the phasedifference over the entire light-shielding film decreases as thethickness of the front-surface antireflection layer decreases.

FIG. 4 shows the relationships between the thickness of thefront-surface antireflection layers and the EMF bias, using the samesimulation results. The EMF bias can be more reduced in the case of thelight-shielding film using the light-shielding layer of Condition 1(n=1.50, k=2.66, d=40 nm) than in the case of the light-shielding filmusing the light-shielding layer of Condition 3 (n=2.00, k=2.58, d=40nm), regardless of the thickness of the front-surface antireflectionlayer. From this result, it is seen that the EMF bias can be morereduced using a material with a smaller refractive index n as thelight-shielding layer. Although the light-shielding layer of Condition 2(n=1.50, k=2.14, d=50 nm) has the same refractive index n as thelight-shielding layer of Condition 1, the EMF bias is greater than inthe case of the light-shielding film using the light-shielding layer ofCondition 3 with the higher refractive index n. The thickness of thelight-shielding layer of Condition 2 is greater by 10 nm than those ofthe light-shielding layers of Conditions 1 and 3. From this result, itis seen that the EMF bias can be more reduced as the thickness of thelight-shielding layer decreases. The reason that the thickness of thelight-shielding layer of Condition 2 is greater than those of thelight-shielding layers of Conditions 1 and 3 is for ensuring apredetermined optical density, which is substantially the same as thoseof the light-shielding layers of Conditions 1 and 3, for thelight-shielding layer of Condition 2 because the extinction coefficientk of the light-shielding layer of Condition 2 is low. From theseresults, it is necessary to select a material with a large extinctioncoefficient k as the material of the light-shielding layer.

Further, simulation was carried out for verifying the influence on anEMF bias only by the difference in the refractive index n and extinctioncoefficient k of light-shielding layers. As simulation conditions,first, the thickness of the light-shielding layers was fixed to 44 nmand the thickness of front-surface antireflection layers was fixed to 4nm. The properties of a material of the front-surface antireflectionlayers were fixed to a refractive index n of 2.35 and an extinctioncoefficient k of 0.99. The illumination condition of ArF exposure lightwas set to annular illumination. With respect to seven kinds oflight-shielding layers having different refractive indices n anddifferent extinction coefficients k, simulation was carried out usingthree kinds of line & space patterns with full pitches of 80 nm, 100 nm,and 120 nm, respectively, as transfer patterns to be exposed andtransferred to objects. FIGS. 5 to 7 are graphs in which, based on theresults of this simulation, differences in EMF bias due to therefractive indices n and extinction coefficients k of thelight-shielding layers are shown by sizes of bubbles with respect to thefull pitches of 80 nm, 100 nm, and 120 nm, respectively. As the size ofthe bubble increases, it means that the EMF bias is larger. From theseresults, it is seen that, regardless of the pitch of the transferpattern, the EMF bias decreases as the refractive index n of thelight-shielding layer decreases or as the extinction coefficient k ofthe light-shielding layer increases.

In a simplified example, in the case of a line & space pattern with afull pitch of 80 nm, the space width is 40 nm. When an EMF bias is 40nm, a space portion is lost on an object upon carrying out exposure andtransfer, meaning that no pattern is exposed or transferred. Taking intoaccount that the transfer pattern is surely exposed and transferred tothe object, the EMF bias is preferably suppressed to ¼ or less of thespace width. In the simulation results, shown in FIG. 2, using the line& space pattern with the full pitch of 80 nm, the EMF bias cannot besuppressed to 10 nm or less in the case of Condition 3 where therefractive index n of the light-shielding layer is 2.00 and in the caseof Condition 2 where the extinction coefficient k of the light-shieldinglayer is 2.14. Even in the case of Condition 1 where the refractiveindex n of the light-shielding layer is 1.50 and the extinctioncoefficient k of the light-shielding layer is 2.66, unless the phasedifference of the light-shielding film is 30 degrees or less, the EMFbias cannot be suppressed to 10 nm or less.

Simulation was carried out for EMF biases in the case of using amaterial with a refractive index n of 1.50 as light-shielding layers andfixing the material and thickness of front-surface antireflectionlayers. A transfer pattern to be exposed and transferred to an objectwas a line & space pattern with a full pitch of 80 nm (space width: 40nm). The illumination condition of ArF exposure light was set to annularillumination. The results of this simulation are shown in FIG. 8. FromFIG. 8, it is seen that, in order to suppress the EMF bias to 10 nm orless, even if the light-shielding layer made of the material with thelow refractive index n is used, the thickness of the entirelight-shielding film should be set to 45 nm or less.

On the other hand, from the results of FIGS. 3 and 4, it has been foundthat, in order to satisfy that the phase difference of thelight-shielding film is set to 30 degrees or less and that the EMF biasin the case of the line & space pattern with the full pitch of 80 nm issuppressed to 10 nm or less, the thickness of the front-surfaceantireflection layer should be set to 6 nm or less. Further, from theresults of FIG. 3, it has also been found that, in order to suppress thefront-surface reflectance of the light-shielding film for exposure lightto less than 50%, the thickness of the front-surface antireflectionlayer should be set to 3 nm or more.

Since the total thickness of the light-shielding film should be set to45 nm or less and the thickness of the front-surface antireflectionlayer should be set to 3 nm or more, the thickness of thelight-shielding layer should be set to 42 nm or less. In order toprovide the front-surface antireflection layer with the function ofreducing the front-surface reflectance, the front-surface antireflectionlayer should be made of a material with a small extinction coefficientk. Therefore, it is preferable that the predetermined optical density(OD) required for the light-shielding film be basically satisfied onlyby the light-shielding layer.

FIG. 9 shows border lines of predetermined optical densities (OD: 2.8and 3.0), wherein the abscissa axis represents the extinctioncoefficient k of the light-shielding layer while the ordinate axisrepresents the thickness of the light-shielding layer. Thelight-shielding film preferably has OD 2.8 or more. In order to ensureOD 2.8 or more with the thickness of the light-shielding layer being theupper limit of 42 nm, the extinction coefficient k should be set to 2.37or more. In order to ensure OD 3.0 or more, the extinction coefficient kshould be set to 2.54 or more. On the other hand, when the thickness ofthe front-surface antireflection layer is set to 6 nm, the upper limitof the thickness of the light-shielding layer should be 39 nm. In thiscase, in order to ensure OD 2.8 or more by the light-shielding layer,the extinction coefficient k should be set to 2.54 or more. In order toensure OD 3.0 or more, the extinction coefficient k should be set to2.73 or more.

When the total thickness of the light-shielding film is 44 nm or less,since the thickness of the front-surface antireflection layer should beset to 3 nm or more, the thickness of the light-shielding layer shouldbe set to 41 nm or less. In this case, in order to ensure OD 2.8 ormore, the extinction coefficient k should be set to 2.42 or more. Inorder to ensure OD 3.0 or more, the extinction coefficient k should beset to 2.58 or more. On the other hand, when the thickness of thefront-surface antireflection layer is set to 6 nm, the upper limit ofthe thickness of the light-shielding layer should be 38 nm. In thiscase, in order to ensure OD 2.8 or more by the light-shielding layer,the extinction coefficient k should be set to 2.60 or more. In order toensure OD 3.0 or more, the extinction coefficient k should be set to2.80 or more.

When the total thickness of the light-shielding film is 42 nm or less,since the thickness of the front-surface antireflection layer should beset to 3 nm or more, the thickness of the light-shielding layer shouldbe set to 39 nm or less. In this case, in order to ensure OD 2.8 ormore, the extinction coefficient k should be set to 2.54 or more. Inorder to ensure OD 3.0 or more, the extinction coefficient k should beset to 2.73 or more. On the other hand, when the thickness of thefront-surface antireflection layer is set to 6 nm, the upper limit ofthe thickness of the light-shielding layer should be 36 nm. In thiscase, in order to ensure OD 2.8 or more by the light-shielding layer,the extinction coefficient k should be set to 2.75 or more. In order toensure OD 3.0 or more, the extinction coefficient k should be set to2.94 or more.

When the total thickness of the light-shielding film is 40 nm or less,since the thickness of the front-surface antireflection layer should beset to 3 nm or more, the thickness of the light-shielding layer shouldbe set to 37 nm or less. In this case, in order to ensure OD 2.8 ormore, the extinction coefficient k should be set to 2.67 or more. Inorder to ensure OD 3.0 or more, the extinction coefficient k should beset to 2.86 or more. On the other hand, when the thickness of thefront-surface antireflection layer is set to 6 nm, the upper limit ofthe thickness of the light-shielding layer should be 34 nm. In thiscase, in order to ensure OD 2.8 or more by the light-shielding layer,the extinction coefficient k should be set to 2.90 or more. In order toensure OD 3.0 or more, the extinction coefficient k should be set to3.10 or more.

The thickness of the light-shielding layer is preferably 30 nm or more.In order to ensure OD 2.8 or more with the thickness of 30 nm, it isnecessary to select a material with an extinction coefficient k of 3.30or more. In particular, in order to ensure OD 3.0 or more, it isnecessary to select a material with an extinction coefficient k of 3.50or more. The materials having such properties are very limited. In orderto reduce the thickness of the light-shielding layer to less than 30 nm,it is necessary to find a material with an extinction coefficient k of3.30 or more, which, however, is difficult.

From the results described above, it is seen that the refractive index nof the light-shielding layer should be less than 2.00. Since the EMFbias can be more reduced as the refractive index n of thelight-shielding layer decreases, it is preferably 1.80 or less, morepreferably 1.60 or less, and optimally 1.50 or less.

From the results of various studies described above, the refractiveindex n of the material forming the light-shielding layer should be lessthan 2.00 and the extinction coefficient k thereof should be 2.37 ormore. A material containing a metal and silicon, particularly a materialcontaining a transition metal and silicon, can have such properties.However, it is necessary to reduce as much as possible an element(particularly, oxygen, nitrogen, carbon, hydrogen, or inert gas (helium,argon, xenon)) that is adapted to increase the refractive index n of thelight-shielding layer or to reduce the extinction coefficient k of thelight-shielding layer. The total content of these elements should belimited to less than 10 at %. Accordingly, the light-shielding layer ispreferably made of a material in which the total content of a metal andsilicon is 90 at % or more, particularly a material in which the totalcontent of a transition metal and silicon is 90 at % or more.

As described above, this invention is an invention aimed at suppressingan EMF bias by reducing the phase difference over the entirelight-shielding film, as compared with conventional, that has nothitherto been paid attention to or controlled in a binary mask or abinary mask blank.

Further, this invention is an invention aimed at suppressing an EMF biasby designing such that the phase difference produced by a front-surfaceantireflection layer becomes small.

Further, this invention is an invention aimed at suppressing an EMF biasby largely reducing, as compared with conventional, the phase differenceproduced by a front-surface antireflection layer.

Further, this invention is an invention aimed at suppressing an EMF biasby considerably reducing, as compared with conventional, the thicknessof a front-surface antireflection layer.

In this invention, also from the results of FIG. 2 and so on, the phasedifference over the entire light-shielding film is preferably 25 degreesor less and more preferably 20 degrees or less in terms of suppressingthe EMF bias.

In this invention, the light-shielding film has a laminated structure ofa light-shielding layer (lower layer) and a front-surface antireflectionlayer (upper layer).

For example, as shown in FIG. 13, a mask blank of this inventioncomprises, on a transparent substrate 1, a light-shielding film 10having a laminated structure of a light-shielding layer (lower layer) 11and a front-surface antireflection layer (upper layer) 12.

In this invention, in terms of improving the problem of theelectromagnetic field (EMF) effect, it is effective to achieve areduction in thickness by the use of the structure having noback-surface antireflection layer. However, the light-shielding film mayhave a structure having another layer (e.g. a back-surfaceantireflection layer) in addition to the light-shielding layer and thefront-surface antireflection layer.

In this invention, as a transition metal (M) forming the light-shieldinglayer, use can be made of one of molybdenum (Mo), tantalum (Ta),chromium (Cr), tungsten (W), titanium (Ti), zirconium (Zr), hafnium(Hf), vanadium (V), niobium (Nb), nickel (Ni), palladium (Pb), iron(Fe), ruthenium (Ru), rhodium (Rh), iridium (Ir), platinum (Pt), zinc(Zn), gold (Au), and silver (Ag), an alloy of two or more of them, orthe like.

In this invention, the front-surface antireflection layer should have athickness of 6 nm or less. In terms of further suppressing the EMF bias,the thickness of the front-surface antireflection layer is preferably 5nm or less and more preferably 4 nm or less.

In this invention, in terms of providing the front-surfaceantireflection layer with the antireflection function, the refractiveindex n of the front-surface antireflection layer should be 2.00 ormore. Further, the refractive index n of the front-surfaceantireflection layer is preferably 2.10 or more and more preferably 2.20or more.

In this invention, in terms of providing the front-surfaceantireflection layer with the antireflection function, the extinctioncoefficient k of the front-surface antireflection layer should be 1.00or less. Further, the extinction coefficient k of the front-surfaceantireflection layer is preferably 0.90 or less and more preferably 0.80or less.

In this invention, the front-surface antireflection layer is a layerformed by deposition for the purpose of preventing the front-surfacereflection. In this invention, the front-surface antireflection layerdoes not have a structure only with a film formed at a surface of thelight-shielding film by surface oxidation, a structure only with a filmformed at a surface of the light-shielding film by heating, or the like.

In this invention, the front-surface reflectance of the light-shieldingfilm for ArF exposure light should be less than 50% and is preferably45% or less and more preferably 40% or less.

In this invention, the ratio obtained by dividing the content of thetransition metal in the light-shielding layer by the total content ofthe transition metal and silicon in the light-shielding layer is 42% orless.

In this invention, the transition metal in the light-shielding layer ispreferably molybdenum (Mo).

FIG. 10 is a graph in which, with respect to molybdenum silicide filmseach made of molybdenum (Mo) as a transition metal and silicon (Si),refractive indices n and extinction coefficients k of materials havingdifferent ratios each obtained by dividing the molybdenum content [at %]in the film by the molybdenum and silicon total content [at %] in thefilm (i.e. the ratio of the molybdenum content in the film when themolybdenum and silicon total content in the film is given as 100;hereinafter referred to as a “Mo/(Mo+Si) ratio”) were measured andplotted. The extinction coefficient k tends to increase to some extentas the Mo/(Mo+Si) ratio increases, but to stop increasing on the way(around 33%). On the other hand, the refractive index n tends toincrease as the Mo/(Mo+Si) ratio increases to at least 50%. As describedabove, the material applicable to the light-shielding layer should havea refractive index n of less than 2.00. When molybdenum silicide is usedas the material of the light-shielding layer, the Mo/(Mo+Si) ratioshould be 42% or less. In order to set the refractive index n of thelight-shielding layer to 1.80 or less, the Mo/(Mo+Si) ratio should beset to 35% or less. In order to set the refractive index n of thelight-shielding layer to 1.60 or less, the Mo/(Mo+Si) ratio should beset to 27% or less. In order to set the refractive index n of thelight-shielding layer to 1.50 or less, the Mo/(Mo+Si) ratio should beset to 23% or less. In the case where elements adapted to increase therefractive index n of the light-shielding layer are contained in thelight-shielding layer in an amount of less than 10 at %, it is necessaryto reduce the refractive index n by the Mo/(Mo+Si) ratio. In this case,it is preferable that the above-mentioned upper limits of the Mo/(Mo+Si)ratio be reduced by about 8%.

Taking into account the extinction coefficient k of the light-shieldinglayer, in order to set the extinction coefficient k to 2.75 or more, theMo/(Mo+Si) ratio should be set to 2% or more from FIG. 10. In order toset the extinction coefficient k to 2.80 or more, the Mo/(Mo+Si) ratioshould be set to 4% or more. In order to set the extinction coefficientk to 2.86 or more, the Mo/(Mo+Si) ratio should be set to 6% or more. Inorder to set the extinction coefficient k to 2.90 or more, theMo/(Mo+Si) ratio should be set to 7% or more. In order to set theextinction coefficient k to 3.00 or more, the Mo/(Mo+Si) ratio should beset to 11% or more. In order to set the extinction coefficient k to 3.10or more, the Mo/(Mo+Si) ratio should be set to 16% or more. Herein, theverification was carried out by selecting the molybdenum silicide as atransition metal silicide, but other transition metal silicides alsoshow substantially the same tendency.

In this invention, the front-surface antireflection layer is preferablycomposed mainly of a material containing a transition metal (M),silicon, and further, at least one element from oxygen and nitrogen, amaterial containing silicon and, further, at least one element fromoxygen and nitrogen, or a material containing a transition metal (M)and, further, at least one element from oxygen and nitrogen. As thetransition metal forming the front-surface antireflection layer, any ofthe above-listed transition metals each usable as the light-shieldinglayer can be used as it is. This is because, in the case where thelight-shielding layer is formed of a material containing the transitionmetal and silicon, both layers can be dry-etched using the same etchinggas and thus excellent etching rate controllability can also beachieved. Further, if the same sputtering target, which is used in theformation of the light-shielding layer, can be used, excellent filmformation throughput can be achieved, which is thus more preferable.

In this invention, the front-surface antireflection layer composedmainly of the material containing the transition metal (M), silicon, andfurther, at least one element from oxygen and nitrogen can be formed ofMSiO, MSiN, MSiON, MSiOC, MSiCN, MSiOCN, or the like.

In this invention, the front-surface antireflection layer composedmainly of the material containing silicon and, further, at least oneelement from oxygen and nitrogen can be formed of SiO, SiN, SiON, SiOC,SiCN, SiOCN, or the like.

In this invention, the front-surface antireflection layer composedmainly of the material containing the transition metal (M) and, further,at least one element from oxygen and nitrogen can be formed of MO, MN,MON, MOC, MCN, MOCN, or the like.

A material composed mainly of Ta (TaO, TaON, TaBO, TaBON, or the like)is preferable as the front-surface antireflection layer.

The front-surface antireflection layer made of tantalum oxide containing50 at % or more oxygen is preferable because it is excellent inantireflection effect.

In this invention, the transition metal in the front-surfaceantireflection layer is preferably molybdenum (Mo). This is becausethere is an advantage such that when the transition metal in thelight-shielding layer is molybdenum (Mo), the front-surfaceantireflection layer can be formed using the same sputtering target usedfor the light-shielding layer.

In this invention, the light-shielding layer made of Mo and Si is freelycontrollable in tensile stress and compressive stress by the gaspressure in a sputtering chamber and a heat treatment. For example, bycontrolling the film stress of the light-shielding layer made of Mo andSi to be a tensile stress, it is possible to achieve balance with thecompressive stress of the front-surface antireflection layer (e.g.MoSiON). That is, it is possible to cancel the stresses of therespective layers forming the light-shielding film and thus to reducethe film stress of the light-shielding film as much as possible (tosubstantially zero).

In this invention, as the front-surface antireflection layer, use can bemade of MoSiON, MoSiO, MoSiN, MoSiOC, MoSiOCN, or the like.

In this invention, if Mo is increased in amount in MoSiON, MoSiO, MoSiN,MoSiOC, MoSiOCN, or the like being the front-surface antireflectionlayer, the cleaning resistance, particularly the resistance to alkali(aqueous ammonia, etc.) or hot water, decreases. From this point ofview, it is preferable to minimize Mo in MoSiON, MoSiO, MoSiN, MoSiOC,MoSiOCN, or the like being the front-surface antireflection layer.

It has been found that, upon carrying out a heat treatment (annealing)at a high temperature for the purpose of stress control, if the Mocontent is high, a phenomenon that a film surface is clouded white(becomes cloudy) occurs. This is considered to be because MoO isprecipitated on the surface. In terms of avoiding such a phenomenon, thecontent of Mo in MoSiON, MoSiO, MoSiN, MoSiOC, MoSiOCN, or the likebeing the front-surface antireflection layer is preferably less than 10at %. However, if the Mo content is too low, abnormal discharge becomessignificant in DC sputtering so that the defect occurrence frequencyincreases. Therefore, it is preferable to contain Mo in a range capableof carrying out sputtering normally. According to another film formingtechnique, there is a case where the film formation is enabled withoutcontaining Mo.

The mask blank of this invention is applicable to a binary mask blankfor use in single exposure, double patterning, or double exposure.

The double patterning is a technique that carries out twice a series ofprocesses of resist coating, exposure, development, and resist strippingwith respect to a semiconductor wafer, thereby carrying out patterning.That is, exposure of a transfer pattern is carried out once with respectto a resist film on the wafer in the same manner as conventional singleexposure, wherein overlapping exposure portions are subjected toexposure of four times at maximum due to leakage light.

The double exposure is a technique that carries out exposure of atransfer pattern onto a resist film on a semiconductor wafer using afirst transfer mask and then carries out exposure of a transfer patternonto the same resist film using a second transfer mask.

A method of manufacturing a transfer mask according to this inventioncomprises an etching step of patterning, by etching, the light-shieldingfilm in any of the mask blanks having the above-mentioned structures.

A binary transfer mask of this invention is adapted to be applied withArF excimer laser exposure light, the transfer mask comprising, on atransparent substrate, a light-shielding film having a transfer pattern,

wherein the light-shielding film has a laminated structure of alight-shielding layer (lower layer) and a front-surface antireflectionlayer (upper layer) and has an optical density of 2.8 or more for theexposure light and a thickness of 45 nm or less,

the light-shielding layer (lower layer) is made of a material in whichthe total content of a transition metal and silicon is 90 at % or more,and has a thickness of 30 nm or more,

the front-surface antireflection layer (upper layer) has a thickness of3 nm or more and 6 nm or less, and

a phase difference between the exposure light transmitted through thelight-shielding film and the exposure light transmitted in air for adistance equal to the thickness of the light-shielding film is 30degrees or less.

A binary transfer mask of this invention is also adapted to be appliedwith ArF excimer laser exposure light, the transfer mask comprising, ona transparent substrate, a light-shielding film having a transferpattern,

wherein the light-shielding film has a laminated structure of alight-shielding layer (lower layer) and a front-surface antireflectionlayer (upper layer) and has an optical density of 2.8 or more for theexposure light and a thickness of 45 nm or less.

the light-shielding layer (lower layer) is made of a material having arefractive index n of less than 2.00 and an extinction coefficient k of2.37 or more and has a thickness of 30 nm or more,

the front-surface antireflection layer (upper layer) has a thickness of3 nm or more and 6 nm or less, and

a phase difference between the exposure light transmitted through thelight-shielding film and the exposure light transmitted in air for adistance equal to the thickness of the light-shielding film is 30degrees or less.

According to the above-mentioned structure, using the mask blank havingthe light-shielding film with a reduced EMF bias, various loads appliedto the manufacture of a transfer mask are largely reduced. Further, theobtained transfer mask can simultaneously satisfy a condition that thelight-shielding film ensures an optical density that can preventsensitization of a resist film on a semiconductor wafer due to leakagelight caused by overlapping exposure.

The transfer mask of this invention is applicable to a transfer mask foruse in single exposure, double patterning, or double exposure.

In this invention, as shown in FIG. 13, it is preferable to provide, onthe light-shielding film 10, an etching mask film 20 made of a materialhaving high etching selectivity to a material of the light-shieldingfilm 10. The line width of a transfer pattern to be formed in thelight-shielding film 10 is as very small as 40 nm in half-pitch in thecase of a line & space pattern. If such a fine pattern is formed in aresist film 100 of an organic material for directly dry-etching thelight-shielding film 10 using the pattern of the resist film 100 as amask, there is a problem that the thickness of the resist film 100becomes too large, so that the pattern transfer accuracy is largelydegraded. In view of this, if the fine pattern formed in the resist film100 is transferred, by dry etching, to the thin etching mask film 20and, using as a mask the etching mask film 20 formed with a transferpattern, the light-shielding film 10 is dry-etched for pattern transfer,a transfer pattern can be formed in the light-shielding film 10 withhigh accuracy. In the case where the light-shielding film 10 isdry-etched using a fluorine-based gas, a material containing chromiumhaving high etching selectivity is preferable as the material of theetching mask film 20. The material containing chromium is normallydry-etched using a mixed gas of chlorine-based gas and oxygen. In orderto improve the etching rate in dry etching of the etching mask film 20made of the material containing chromium, the content of chromium in theetching mask film 20 is preferably 45 at % or less, further preferably40 at % or less, and more preferably 35 at % or less.

In this invention, for dry-etching a thin film containing a transitionmetal and silicon or a thin film containing a transition metal, use canbe made of, for example, a fluorine-based gas such as SF₆, CF₄, C₂F₆, orCHF₃, a mixed gas of such a fluorine-based gas and He, H₂, N₂, Ar, C₂H₄,O₂ or the like, a chlorine-based gas such as Cl₂ or CH₂Cl₂, or a mixedgas of such a chlorine-based gas and He, H₂, N₂, Ar, C₂H₄, or the like.

In this invention, the resist is preferably a chemically amplifiedresist. The reason is that the chemically amplified resist is suitablefor high-accuracy processing.

This invention is applied to mask blanks of the generations aimed at aresist film thickness of 100 nm or less, a resist film thickness of 75nm or less, and further a resist film thickness of 50 nm.

In this invention, the resist may alternatively be a resist for electronbeam writing. The reason is that the resist for electron beam writing isalso suitable for high-accuracy processing.

This invention is applied to an electron beam writing mask blank adaptedto be formed with a resist pattern by electron beam writing.

In this invention, as the transparent substrate, use can be made of asynthetic quartz substrate, a CaF₂ substrate, a soda-lime glasssubstrate, an alkali-free glass substrate, a low thermal expansion glasssubstrate, an aluminosilicate glass substrate, or the like.

In this invention, the mask blank may be a binary mask blank or aresist-coated mask blank.

In this invention, the transfer mask may be a binary mask which does notuse the phase shift effect, or may be a reticle. In this invention, anenhancer mask and a phase shift mask are not included.

A method of manufacturing a semiconductor device according to thisinvention is characterized by forming a circuit pattern on asemiconductor wafer using the binary transfer mask according to any ofthe above-mentioned Structures.

Further, the method of manufacturing the semiconductor device of thisinvention is characterized in that the circuit pattern formed on thesemiconductor wafer includes a line & space pattern of half-pitch 40 nmor less.

The transfer mask of this invention is excellent in transfer accuracy ofa line & space pattern of half-pitch 40 nm or less and is most suitablefor forming on a semiconductor wafer a circuit pattern having a line &space pattern of half-pitch 40 nm or less.

EXAMPLES

Hereinbelow, this invention will be described in more detail withreference to Examples.

Example 1

(Manufacture of Mask Blank)

As shown in FIG. 13, using a synthetic quartz glass substrate having a6-inch square size with a thickness of 0.25 inches as a transparentsubstrate 1, a MoSiN film (light-shielding layer 11: lower layer) and aMoSiON film (front-surface antireflection layer 12: upper layer) wereformed in this order as a light-shielding film 10 on the transparentsubstrate 1.

Specifically, using a mixed target of molybdenum (Mo) and silicon (Si)(Mo:Si=21 at %:79 at %), reactive sputtering (DC sputtering) was carriedout in a mixed gas atmosphere of argon (Ar) and nitrogen (N₂), therebyforming the light-shielding layer 11 (MoSiN film, N=about 5 at %) to athickness of 35 nm on the transparent substrate 1.

Then, using a mixed target of molybdenum (Mo) and silicon (Si) (Mo:Si=4at %:96 at %), reactive sputtering (DC sputtering) was carried out in amixed gas atmosphere of argon (Ar), oxygen (O₂), and nitrogen (N₂),thereby forming the front-surface antireflection layer 12 (MoSiON film)to a thickness of 4 nm on the light-shielding layer 11.

The total thickness of the light-shielding film 10 was set to 39 nm. Theoptical density (OD) of the light-shielding film 10 was 3.03 at thewavelength 193 nm of ArF excimer laser exposure light.

The front-surface reflectance of the light-shielding film 10 was 41.9%.The transmittance and the reflectance were measured using aspectrophotometer.

The MoSiN film (light-shielding layer 11: lower layer) had a refractiveindex n of 1.50 and an extinction coefficient k of 3.06.

The MoSiON film (front-surface antireflection layer 12: upper layer) hada refractive index n of 2.28 and an extinction coefficient k of 0.92.

(Heat Treatment after Film Formation)

Then, the above-mentioned substrate was heat-treated (annealed) at 450°C. for 30 minutes.

(Evaluation)

The phase difference (phase shift angle) between exposure lighttransmitted through the light-shielding film 10 and exposure lighttransmitted in air for a distance equal to the thickness of thelight-shielding film 10 was examined and, as a result, it was 13degrees.

FIG. 11 is a graph showing the results of examining how the totalthickness, the total phase shift amount, the total OD, and thefront-surface reflectance respectively change when the upper layerthickness and the lower layer thickness are respectively changed inExample 1.

From FIG. 11, it is seen that it is necessary to synthetically study andconsider the upper layer thickness (AR layer thickness), the lower layerthickness (light-shielding layer thickness), the total thickness, thetotal phase shift amount, the total OD, and the front-surfacereflectance (% R).

Before manufacturing a binary transfer mask adapted to be applied withArF exposure light and having a transfer pattern including a line &space pattern (L&S) of DRAM half-pitch (hp) 40 nm according to thesemiconductor device design rule, simulation for examining an EMF biaswas carried out using a mask blank of Example 1. As a result, the EMFbias was 6.2 nm in the case of annular illumination and was −0.3 nm inthe case of dipole illumination.

Example 2

(Manufacture of Mask Blank)

As shown in FIG. 13, using a synthetic quartz glass substrate having a6-inch square size with a thickness of 0.25 inches as a transparentsubstrate 1, a MoSi film (light-shielding layer 11: lower layer) and aMoSiON film (front-surface antireflection layer 12: upper layer) wereformed in this order as a light-shielding film 10 on the transparentsubstrate 1.

Specifically, using a mixed target of molybdenum (Mo) and silicon (Si)(Mo:Si=9.5 at %:89.5 at %), sputtering (DC sputtering) was carried outin an argon (Ar) gas atmosphere, thereby forming the light-shieldinglayer 11 (MoSi film) to a thickness of 38 nm on the transparentsubstrate 1.

Then, using a mixed target of molybdenum (Mo) and silicon (Si) (Mo:Si=4at %:96 at %), reactive sputtering (DC sputtering) was carried out in amixed gas atmosphere of argon (Ar), oxygen (O₂), and nitrogen (N₂),thereby forming the front-surface antireflection layer 12 (MoSiON film)to a thickness of 4 nm on the light-shielding layer 11.

The total thickness of the light-shielding film 10 was set to 42 nm. Theoptical density (OD) of the light-shielding film 10 was 3.0 at thewavelength 193 nm of ArF excimer laser exposure light.

The front-surface reflectance of the light-shielding film 10 was 39.6%.The transmittance and the reflectance were measured using aspectrophotometer.

The MoSi film (light-shielding layer 11: lower layer) had a refractiveindex n of 1.24 and an extinction coefficient k of 2.77.

The MoSiON film (front-surface antireflection layer 12: upper layer) hada refractive index n of 2.28 and an extinction coefficient k of 0.92.

(Heat Treatment after Film Formation)

Then, the above-mentioned substrate was heat-treated (annealed) at 450°C. for 30 minutes.

(Evaluation)

The phase difference (phase shift angle) between exposure lighttransmitted through the light-shielding film 10 and exposure lighttransmitted in air for a distance equal to the thickness of thelight-shielding film 10 was examined and, as a result, it was 1.1degrees.

FIG. 12 is a graph showing the results of examining how the totalthickness, the total phase shift amount, the total OD, and thefront-surface reflectance respectively change when the upper layerthickness and the lower layer thickness are respectively changed inExample 2.

From FIG. 12, it is seen that it is necessary to synthetically study andconsider the upper layer thickness, the lower layer thickness, the totalthickness, the total phase shift amount, the total OD, and thefront-surface reflectance.

Before manufacturing a binary transfer mask adapted to be applied withArF exposure light and having a transfer pattern including L&S of DRAMhalf-pitch (hp) 40 nm according to the semiconductor device design rule,simulation for examining an EMF bias was carried out using a mask blankof Example 2. As a result, the EMF bias was 6.0 nm in the case ofannular illumination and was −0.5 nm in the case of dipole illumination.

Example 3

(Manufacture of Mask Blank)

As shown in FIG. 13, using a synthetic quartz glass substrate having a6-inch square size with a thickness of 0.25 inches as a transparentsubstrate 1, a MoSi film (light-shielding layer 11: lower layer) and aMoSiON film (front-surface antireflection layer 12: upper layer) wereformed in this order as a light-shielding film 10 on the transparentsubstrate 1.

Specifically, using a mixed target of molybdenum (Mo) and silicon (Si)(Mo:Si=9.5 at %:89.5 at %), sputtering (DC sputtering) was carried outin an argon (Ar) gas atmosphere, thereby forming the light-shieldinglayer 11 (MoSi film) to a thickness of 39 nm on the transparentsubstrate 1.

Then, using a mixed target of molybdenum (Mo) and silicon (Si) (Mo:Si=4at %:96 at %), reactive sputtering (DC sputtering) was carried out in amixed gas atmosphere of argon (Ar), oxygen (O₂), and nitrogen (N₂),thereby forming the front-surface antireflection layer 12 (MoSiON film)to a thickness of 6 nm on the light-shielding layer 11.

The total thickness of the light-shielding film 10 was set to 45 nm. Theoptical density (OD) of the light-shielding film 10 was 3.04 at thewavelength 193 nm of ArF excimer laser exposure light.

The front-surface reflectance of the light-shielding film 10 was 29.8%.The transmittance and the reflectance were measured using aspectrophotometer.

The MoSi film (light-shielding layer 11: lower layer) had a refractiveindex n of 1.24 and an extinction coefficient k of 2.77.

The MoSiON film (front-surface antireflection layer 12: upper layer) hada refractive index n of 2.28 and an extinction coefficient k of 0.92.

(Heat Treatment after Film Formation)

Then, the above-mentioned substrate was heat-treated (annealed) at 450°C. for 30 minutes.

(Evaluation)

The phase difference (phase shift angle) between exposure lighttransmitted through the light-shielding film 10 and exposure lighttransmitted in air for a distance equal to the thickness of thelight-shielding film 10 was examined and, as a result, it was 9.5degrees.

Before manufacturing a binary transfer mask adapted to be applied withArF exposure light and having a transfer pattern including L&S of DRAMhalf-pitch (hp) 40 nm according to the semiconductor device design rule,simulation for examining an EMF bias was carried out using a mask blankof Example 3. As a result, the EMF bias was 7.4 nm in the case ofannular illumination and was −0.1 nm in the case of dipole illumination.

Comparative Example 1

(Manufacture of Mask Blank)

As shown in FIG. 13, using a synthetic quartz glass substrate having a6-inch square size with a thickness of 0.25 inches as a transparentsubstrate 1, a MoSiN film (light-shielding layer 11) and a MoSiON film(front-surface antireflection layer 12) were formed in this order as alight-shielding film 10 on the transparent substrate 1.

Specifically, using a mixed target of molybdenum (Mo) and silicon (Si)(Mo:Si=21 at %:79 at %), reactive sputtering (DC sputtering) was carriedout in a mixed gas atmosphere of argon (Ar) and nitrogen (N₂), therebyforming the light-shielding layer 11 (MoSiN film) to a thickness of 50nm on the transparent substrate 1.

Then, using a mixed target of molybdenum (Mo) and silicon (Si) (Mo:Si=4at %:96 at %), reactive sputtering (DC sputtering) was carried out in amixed gas atmosphere of argon (Ar), oxygen (O₂), and nitrogen (N₂),thereby forming the front-surface antireflection layer 12 (MoSiON film)to a thickness of 10 nm on the light-shielding layer 11.

The elements of the respective layers were analyzed by the Rutherfordbackscattering spectrometry.

The total thickness of the light-shielding film 10 was set to 60 nm. Theoptical density (OD) of the light-shielding film 10 was 3.0 at thewavelength 193 nm of ArF excimer laser exposure light.

The front-surface reflectance of the light-shielding film 10 was 21.3%.The transmittance and the reflectance were measured using aspectrophotometer.

The MoSiN film (light-shielding layer 11) had a refractive index n of2.42 and an extinction coefficient k of 1.91.

The MoSiON film (front-surface antireflection layer 12) had a refractiveindex n of 2.31 and an extinction coefficient k of 1.00.

(Heat Treatment after Film Formation)

Then, the above-mentioned substrate was heat-treated (annealed) at 450°C. for 30 minutes.

(Evaluation)

The phase difference (phase shift angle) between exposure lighttransmitted through the light-shielding film 10 and exposure lighttransmitted in air for a distance equal to the thickness of thelight-shielding film 10 was examined and, as a result, it was 143degrees.

Before manufacturing a binary transfer mask adapted to be applied withArF exposure light and having a transfer pattern including L&S of DRAMhalf-pitch (hp) 40 nm according to the semiconductor device design rule,simulation for examining an EMF bias was carried out using a mask blankof Comparative Example 1. As a result, the EMF bias was 23.8 nm in thecase of annular illumination and was 4.0 nm in the case of dipoleillumination. In the case of annular illumination, the EMF bias becomes20 nm or more and thus effective bias correction cannot be carried out.That is, it has been seen that, with the mask blank of ComparativeExample 1, a transfer pattern including L&S of DRAM half-pitch (hp) 40nm cannot be formed for a transfer mask which is subjected to annularillumination.

(Manufacture of Transfer Mask)

Referring to FIGS. 13 and 14, an etching mask film 20 was formed on eachof the mask blanks obtained in Examples 1 to 3. Specifically, using achromium target, sputtering (DC sputtering) was carried out in a mixedgas atmosphere of argon (Ar), carbon dioxide (CO₂), nitrogen (N₂), andhelium (He), thereby forming the etching mask film 20 (CrOCN film, Cr:35at %) to a thickness of 10 nm on the light-shielding film 10(front-surface antireflection layer 12). Further, the etching mask film20 was annealed at a temperature lower than the annealing temperature ofthe light-shielding film 10, thereby adjusting the film stress of theetching mask film 20 to be as small as possible (preferably,substantially zero) without affecting the film stress of thelight-shielding film 10.

Then, a chemically amplified positive resist for electron beam writing(PRL009: manufactured by FUJIFILM Electronic Materials Co., Ltd.) wascoated on the etching mask film 20 to form a resist film 100 (see FIG.13 and FIG. 14, (1)). The resist film 100 was formed by spin coatingusing a spinner (spin coating apparatus).

Then, using an electron beam writing apparatus, a transfer patternincluding L&S of DRAM half-pitch (hp) 40 nm was written on the resistfilm 100 and, thereafter, the resist film 100 was developed with apredetermined developer, thereby forming a resist pattern 100 a (seeFIG. 14, (2)),

Then, using the resist pattern 100 a as a mask, the etching mask film 20was dry-etched, thereby forming an etching mask film pattern 20 a (seeFIG. 14, (3)). In this event, a mixed gas of chlorine and oxygen(Cl₂:O₂=4:1) was used as a dry etching gas for the etching mask film 20made of CrOCN.

Then, the remaining resist pattern 100 a was stripped by ashing or thelike (see FIG. 14, (4)).

Then, using the etching mask film pattern 20 a as a mask, thelight-shielding film 10 was dry-etched, thereby forming alight-shielding film pattern 10 a (see FIG. 14, (5)). In this event, amixed gas of SF₆ and He was used as a dry etching gas for the MoSi-basedlight-shielding film 10 (the light-shielding layer 11 and thefront-surface antireflection layer 12).

Finally, the etching mask film pattern 20 a was removed using a mixedgas of chlorine and oxygen (Cl₂:O₂=4:1), thereby obtaining a binarytransfer mask (see FIG. 14, (6)).

Then, using each of the binary transfer masks obtained in Examples 1 to3, a transfer pattern was exposed and transferred to a resist film on asemiconductor wafer as a transfer object. An exposure apparatus was ofthe immersion type with annular illumination using an ArF excimer laseras a light source. Specifically, by setting the binary transfer mask ofExample 1 on a mask stage of the exposure apparatus, a transfer patternwas exposed and transferred to an ArF immersion exposure resist filmformed on a semiconductor wafer. Then, the exposed resist film wasdeveloped, thereby forming a resist pattern. Then, using the resistpattern, a circuit pattern including L&S of DRAM half-pitch (hp) 40 nmwas formed on the semiconductor wafer.

Likewise, with respect to the binary transfer masks of Examples 2 and 3,exposure, transfer, and other processes were carried out in the samemanner for ArF immersion exposure resist films on other semiconductorwafers, thereby forming circuit patterns including L&S of DRAMhalf-pitch (hp) 40 nm on the semiconductor wafers, respectively.

The obtained circuit patterns on the semiconductor wafers of Examples 1to 3 were observed using a transmission electron microscope (TEM). As aresult, all the circuit patterns fully satisfied the specification ofL&S of DRAM half-pitch (hp) 40 nm. That is, it was confirmed that thebinary transfer masks of Examples 1 to 3 were fully able to transfercircuit patterns including LAS of DRAM half-pitch (hp) 40 nm ontosemiconductor wafers, respectively, even in the case of such an exposuretype using annular illumination as a light source.

While this invention has been described with reference to the embodimentand Examples, the technical scope of the invention is not limited to thescope of the description of the above-mentioned embodiment and Examples.It is obvious to a person skilled in the art that various changes orimprovements can be added to the above-mentioned embodiment andExamples. It is clear from the description of claims that the modesadded with such changes or improvements can also be included in thetechnical scope of this invention.

1. A mask blank for use in the manufacture of a binary mask adapted tobe applied with ArF excimer laser exposure light, the mask blankcomprising, on a transparent substrate, a light-shielding film forforming a transfer pattern, wherein the light-shielding film has alaminated structure of a lower layer and an upper layer and has anoptical density of 2.8 or more for the exposure light and a thickness of45 nm or less, the lower layer is made of a material in which the totalcontent of a transition metal and silicon is 90 at % or more, and has athickness of 30 nm or more, the upper layer has a thickness of 3 nm ormore and 6 nm or less, and a phase difference between the exposure lighttransmitted through the light-shielding film and the exposure lighttransmitted in air for a distance equal to the thickness of thelight-shielding film is 30 degrees or less.
 2. The mask blank accordingto claim 1, wherein a ratio obtained by dividing a content of thetransition metal in the lower layer by the total content of thetransition metal and silicon in the lower layer is 42% or less.
 3. Themask blank according to claim 1, wherein the transition metal in thelower layer is molybdenum (Mo).
 4. The mask blank according to claim 1,wherein the upper layer is made of a material having a refractive indexn of 2.00 or more and an extinction coefficient k of 1.00 or less. 5.The mask blank according to claim 1, wherein the lower layer has athickness of 42 nm or less.
 6. The mask blank according to claim 1,wherein the upper layer is made of: a material containing a transitionmetal, silicon, and at least one element from oxygen and nitrogen, amaterial containing silicon and at least one element from oxygen andnitrogen, or a material containing a transition metal and at least oneelement from oxygen and nitrogen.
 7. The mask blank according to claim6, wherein the transition metal in the upper layer is molybdenum (Mo).8. A method of manufacturing a transfer mask, comprising an etching stepof patterning, by etching, the light-shielding film in the mask blankaccording to claim
 1. 9. A mask blank for use in the manufacture of abinary mask adapted to be applied with ArF excimer laser exposure light,the mask blank comprising, on a transparent substrate, a light-shieldingfilm for forming a transfer pattern, wherein the light-shielding filmhas a laminated structure of a lower layer and an upper layer and has anoptical density of 2.8 or more for the exposure light and a thickness of45 nm or less, the lower layer is made of a material having a refractiveindex n of less than 2.00 and an extinction coefficient k of 2.37 ormore and has a thickness of 30 nm or more, the upper layer has athickness of 3 nm or more and 6 nm or less, and a phase differencebetween the exposure light transmitted through the light-shielding filmand the exposure light transmitted in air for a distance equal to thethickness of the light-shielding film is 30 degrees or less.
 10. Themask blank according to claim 9, wherein the upper layer is made of amaterial having a refractive index n of 2.00 or more and an extinctioncoefficient k of 1.00 or less.
 11. The mask blank according to claim 9,wherein the lower layer has a thickness of 42 nm or less.
 12. The maskblank according to claim 9, wherein the upper layer is made of: amaterial containing a transition metal, silicon, and at least oneelement from oxygen and nitrogen, a material containing silicon and atleast one element from oxygen and nitrogen, or a material containing atransition metal and at least one element from oxygen and nitrogen. 13.The mask blank according to claim 12, wherein the transition metal inthe upper layer is molybdenum (Mo).
 14. A method of manufacturing atransfer mask, comprising an etching step of patterning, by etching, thelight-shielding film in the mask blank according to claim
 9. 15. Abinary transfer mask adapted to be applied with ArF excimer laserexposure light, the transfer mask comprising, on a transparentsubstrate, a light-shielding film having a transfer pattern, wherein thelight-shielding film has a laminated structure of a lower layer and anupper layer and has an optical density of 2.8 or more for the exposurelight and a thickness of 45 nm or less, the lower layer is made of amaterial in which the total content of a transition metal and silicon is90 at % or more, and has a thickness of 30 nm or more, the upper layerhas a thickness of 3 nm or more and 6 nm or less, and a phase differencebetween the exposure light transmitted through the light-shielding filmand the exposure light transmitted in air for a distance equal to thethickness of the light-shielding film is 30 degrees or less.
 16. Abinary transfer mask adapted to be applied with ArF excimer laserexposure light, the transfer mask comprising, on a transparentsubstrate, a light-shielding film having a transfer pattern, wherein thelight-shielding film has a laminated structure of a lower layer and anupper layer and has an optical density of 2.8 or more for the exposurelight and a thickness of 45 nm or less, the lower layer is made of amaterial having a refractive index n of less than 2.00 and an extinctioncoefficient k of 2.37 or more and has a thickness of 30 nm or more, theupper layer has a thickness of 3 nm or more and 6 nm or less, and aphase difference between the exposure light transmitted through thelight-shielding film and the exposure light transmitted in air for adistance equal to the thickness of the light-shielding film is 30degrees or less.
 17. The binary transfer mask according to claim 15,wherein the transfer pattern of the light-shielding film includes a line& space pattern of half-pitch 40 nm or less.
 18. A method ofmanufacturing a semiconductor device, comprising forming a circuitpattern on a semiconductor wafer using the binary transfer maskaccording to claim
 15. 19. The method according to claim 18, wherein thecircuit pattern formed on the semiconductor wafer includes a line &space pattern of half-pitch 40 nm or less.
 20. The binary transfer maskaccording to claim 16, wherein the transfer pattern of thelight-shielding film includes a line & space pattern of half-pitch 40 nmor less.
 21. A method of manufacturing a semiconductor device,comprising forming a circuit pattern on a semiconductor wafer using thebinary transfer mask according to claim
 16. 22. The method according toclaim 21, wherein the circuit pattern formed on the semiconductor waferincludes a line & space pattern of half-pitch 40 nm or less.